The present invention relates to an optical pick in an optical disc device, and an optical component used therefore, and in particular to a compatible optical pickup in an optical data recording device, which is capable of compatibly accepting not less than 2 standards.
As the standards of optical discs becomes more various, light sources for emitting not less than three light beams having different wavelengths (an infrared beam, a red beam and a blue beam and the like) are used, and demands for compatible optical pickups capable of accepting more various disc standards having been more and more increased on the market. The larger the number of wavelengths/standards, the more complicate the optical systems, and accordingly, the size of the pickups becomes larger, possibly resulting in difficulty in miniaturization of optical pickups.
In order to solve the above-mentioned problems, there has been proposed, for example, such a manner that a semiconductor laser serving as a light source is commonly used so as to lower the costs. As disclosed in JP-A-9-223327, a two standard compatible pickup which commonly uses a light source through polarization changeover has been proposed, as a compatible pickup structure capable of accepting two kinds of disc standards with the use of infrared ray.
Since the wavelengths of laser beams used for light sources have been less and less (from an infrared beam to a red beams and then to a blue beam), pickups capable of accepting not only two kinds but also more kinds of disc standards have been now demanded on the market.
Meanwhile, since it is necessary to maintain a satisfactory servo function, the number of objective lenses set on a single drive carriage is limited, and at present, the number of objective lens which can be set on one drive carriage is in general up to about two. In this case, since a single lens has to accept a plurality of wavelengths, a plurality of semiconductor lenses serving as light sources are used, and an optical path has to be split/synthesized on the way. However, if the optical path is split/synthesized, the optical axial angles are likely to be deviated among the optical axes (relative tilt angles), possibly resulting in asymmetric (unbalance) jitter characteristics of a pickup or occurrence of errors (in particular, tilt dependency). Further, the multiple wavelength compatible pickup as stated above, inevitably causes the optical system to be complicated, and accordingly cannot be small-sized.
Further, for high density optical discs with a blue beam light source, there have been manifested problems such that slight assembly errors of optical components would cause the characteristics to be remarkably unbalance, and the characteristic would be likely deteriorated due to aging effects/temperature variation.
As stated above, since the compatible optical pickup has a plurality of optical axes, if the degree of matching accuracy as to center positions/angles among the optical axes is not higher, deviations of relative tilt of the optical axes and uneven pickup characteristics (unbalance and asymmetry) would be likely caused.